Effects of Human Fecal Flora on Intestinal Morphology and Mucosal Immunity in Human Flora-associated Piglet

Validation of a Combined In Vivo/In Vitro Ileal Fermentation Assay in the Growing Pig to be Used as a Model for Adult Humans

BACKGROUND

An in vivo/in vitro ileal fermentation assay using growing pigs has been developed but not yet formally validated.

OBJECTIVES

This study aimed to validate the in vivo/in vitro ileal fermentation assay by comparing in vitro fermentation values with those obtained in vivo in growing pigs. The effect of raising pigs under different environmental conditions was also investigated.

METHODS

Thirty piglets (1.59 ± 0.31 kg body weight, mean ± standard deviation) were subjected to 1 of 3 treatments: artificially reared (AR) (nonfarm, laboratory housing conditions) from postnatal day (PND) 7 (AR group), inoculated orally with human infant fecal extracts from birth until PND 8 and AR (AR+ group), or conventionally reared on a farm (control group). Starting at PND 7, the AR and AR+ pigs received human infant formula for 3 wk, followed by a human-type diet for 5 wk. Control pigs were weaned on the farm and, on PND 63, relocated to the laboratory animal facility. From PND 63, all pigs received a human-type diet. On PND 78, pigs were killed, after which ileal digesta were collected to perform an in vitro ileal fermentation (in vitro organic matter [OM] fermentability and organic acid production) and to determine digesta microbial composition and dietary OM fermentability in vivo.

RESULTS

The rearing regimen resulted in only a few differences in ileal microbial taxonomic composition. The rearing regimen generally did not affect the in vitro production of individual organic acids. The in vivo and in vitro OM fermentability of proximal ileal digesta (19.7 ± 2.04%; mean ± SEM) was similar (P > 0.05) for the AR and control pigs but not for the AR+ pigs.

CONCLUSIONS

The control-rearing regimen was preferred over AR or AR+ because of ease of implementation. The in vitro ileal fermentation assay accurately predicted the in vivo OM fermentability.

Probiotic Lactobacillus johnsonii BS15 Prevents Memory Dysfunction Induced by Chronic High-Fluorine Intake through Modulating Intestinal Environment and Improving Gut Development

In recent years, the influence of chronic fluorosis on the brain has been widely reported. Our study aimed to demonstrate the potential mechanism underlying the impairment of memory function by excessive fluorine intake. We also evaluated whether improvement of intestinal microflora could be a potential therapy to prevent the negative influences from the perspective of gut-brain axis. Male ICR mice were randomly divided into three groups and administered with either phosphate buffered saline (PBS) (Control and F groups) or Lactobacillus johnsonii BS15 (FP group; daily amounts of 1 × 10⁹ CFU/mL), a probiotic strain, by oral gavage throughout a 98-day experimental period. Sodium fluoride (100 mg/L) was added to the drinking water of the F and FP groups. Animals were sacrificed for sampling with or without water avoidance stress (WAS) at two phases of the experiment and behavioral tests including T-maze test and passive avoidance test were also performed. Based on the results of behavioral tests, probiotic reversed the fluorine-induced memory dysfunction. In addition, L. johnsonii BS15 also increased the antioxidant capacities (serum and hippocampal tissue) and hippocampal synaptic plasticity-related mRNA expression after excessive fluoride ingestion. Moreover, the increased colonization of L. johnsonii BS15 also protected the small intestines from the damages of growth performance, visceral indexes, intestinal development, digestive, and secretory functions by changing the structure of the microflora and then improving intestinal permeability and integrity. L. johnsonii BS15 also improved the ability of flourosis mice against psychological stress indicated by the changes in behavioral tasks, hippocampal antioxidant levels, and synaptic plasticity-related mRNA expressions. Lactobacillus johnsonii BS15 intake appears as a promising way to ameliorate fluorine-induced memory dysfunction, especially under psychological stress.

A piglet model of iatrogenic rectosigmoid hypoganglionosis reveals the impact of the enteric nervous system on gut barrier function and microbiota postnatal development

BACKGROUND

Hirschsprung-associated enterocolitis physiopathology likely involves disturbed interactions between gut microbes and the host during the early neonatal period. Our objective was to create a neonatal porcine model of iatrogenic aganglionosis to evaluate the impact of the enteric nervous system (ENS) on microbiota and intestinal barrier postnatal development.

METHODS

Under general anesthesia, the rectosigmoid serosa of 5-day-old suckling piglets was exposed to 0.5% benzalkonium chloride solution (BAC, n = 7) or saline (SHAM, n = 5) for 1 h. After surgery, animals returned to their home-cage with the sow and littermates and were studied 21 days later.

RESULTS

BAC treatment induced partial aganglionosis with absence of myenteric plexus and reduced surface area of submucosal plexus ganglia (-58%, P < 0.05) in one third of the rectosigmoid circumference. Epithelial permeability of this zone was increased (conductance +63%, FITC-dextran flux +386%, horseradish-peroxidase flux +563%, P < 0.05). Tight junction protein remodeling was observed with decreased ZO-1 (-95%, P < 0.05) and increased claudin-3 and e-cadherin expressions (+197% and 61%, P < 0.05 and P = 0.06, respectively). BAC piglets harbored greater abundance of proinflammatory bacteria (Bilophila, Fusobacterium) compared to SHAM in the rectosigmoid lumen.

CONCLUSIONS

This large animal model demonstrates that hypoganglionosis is associated with dramatic defects of gut barrier function and establishment of proinflammatory bacteria.

Color of Colon Content of Normal and Intrauterine Growth-Restricted Weaned Piglets is Associated with Specific Microbial Taxa and Physiological Parameters

Simple Summary

Selection for hyperprolific sows has increased litter sizes but has also increased the number of small piglets per litter. A large percentage of these piglets have been exposed to intrauterine growth restriction (IUGR) during gestation, and this is accompanied by higher mortality and reduced growth in pig production. In humans, IUGR is associated with long-term health consequences such as cardiovascular disease, as well as metabolic diseases such as type 2 diabetes. It is therefore of interest to study the gut microbiota (GM) of IUGR compared to normal piglets, as a well-balanced GM is associated with improved health outcomes. Differences in feces color was associated with different metabolite signatures and specific GM signatures. Understanding these differences in the composition of the microbial community and its functional capacity during weaning is important for pig production, as the GM play important roles in pig health and growth performance.

Abstract

A well-balanced gut microbiome is associated with improved health outcomes, but to date, the GM of IUGR piglets have only been sparsely investigated. Here, we investigated GM composition, color of colon content, and blood parameters of 20 IUGR and 20 normal 24-day-old piglets. No significant differences were detected in colon microbiota composition between IUGR and the normal piglets with respect to alpha and beta diversity measures. The colon content of these piglets displayed three colors: brown, black, and yellow. Interestingly, the color of the colon content varied with microbial community composition, with significant differences in the relative abundance of taxa belonging to Fusobacteria and Treponema. Fusobacteria were most abundant in yellow fecal samples, with a mean relative abundance around 5.6%, whereas this was 0.51% within brown and 0.02% for the black fecal samples. Fusobacteria positively correlated with total blood protein, albumin, and triglycerides. Contrarily, Treponema was at 0.9% the most abundant in black fecal samples, while present at 0.1% of relative abundance in brown fecal samples and 0.01% in yellow samples, correlating positively with blood iron content. This study indicates that colon/fecal content color can be used as indicator for specific GM and metabolite signatures.

Immune response in piglets orally immunized with recombinant Bacillus subtilis expressing the capsid protein of porcine circovirus type 2

BACKGROUND

Porcine circovirus type 2 (PCV2) is the causative agent of postweaning multisystemic wasting syndrome, and is associated with a number of other diseases. PCV2 is widely distributed in most developed swine industries, and is a severe economic burden. With an eye to developing an effective, safe, and convenient vaccine against PCV2-associated diseases, we have constructed a recombinant Bacillus subtilis strain (B. subtilis-Cap) that expresses the PCV2 capsid protein (Cap).

METHODS

Electroporation of a plasmid shuttle vector encoding the PCV2 Cap sequence was use to transform Bacillus subtilis. Flow cytometry was used to evaluate in vitro bone marrow derived dendritic cell (BM-DC) maturation and T cell proliferation induced by B. subtilis-Cap. Orally inoculated piglets were used for in vivo experiments; ELISA and western blotting were used to evaluate B. subtilis-Cap induced PCV2-specific IgA and IgG levels, as well as the secretion of cytokines and the expression of Toll-like receptor 2 (TLR2) and Toll-like receptor 9 (TLR9).

RESULTS

We evaluated the immune response to B. subtilis-Cap in vitro using mouse BM-DCs and in vivo using neonatal piglets orally inoculated with B. subtilis-Cap. Our results showed that the recombinant B. subtilis-Cap activated BM-DCs, significantly increased co-stimulatory molecules (CD40 and CD80) and major histocompatibility complex II, and induced allogenic T cells proliferation. Piglets immunized with B. subtilis-Cap had elevated levels of PCV2-specific IgA in the mucosal tissues of the digestive and respiratory tract, and PCV2-specific IgG in serum (P < 0.05 or P < 0.01). Ileal immunocompetent cells, such as the IgA-secreting cells (P < 0.01), intestinal intraepithelial lymphocytes (IELs) (P < 0.01), CD3+ T lymphocytes (P < 0.01) and CD4+ T lymphocytes (P < 0.01) increased significantly in the B. subtilis-Cap immunized piglets. Additionally, B. subtilis-Cap inoculation resulted in increased the expression of TLR2 and TLR9 (P < 0.01), and induced the secretion of cytokines IL-1β, IL-6, interferon-γ, and β-defensin 2 (P < 0.01).

CONCLUSIONS

We constructed a prototype PCV2 vaccine that can be administered orally and elicits a more robust humoral and cellular immunity than inactivated PCV2. B. subtilis-Cap is a promising vaccine candidate that is safe, convenient, and inexpensive. Further in vivo research is needed to determine its full range of efficacy in pigs.

A new method for quantitative detection of Lactobacillus casei based on casx gene and its application

Background

The traditional method of bacterial identification based on 16S rRNA is a widely used and very effective detection method, but this method still has some deficiencies, especially in the identification of closely related strains. A high homology with little differences is mostly observed in the 16S sequence of closely related bacteria, which results in difficulty to distinguish them by 16S rRNA-based detection method. In order to develop a rapid and accurate method of bacterial identification, we studied the possibility of identifying bacteria with other characteristic fragments without the use of 16S rRNA as detection targets.

Results

We analyzed the potential of using cas (CRISPR-associated proteins) gene as a target for bacteria detection. We found that certain fragment located in the casx gene was species-specific and could be used as a specific target gene. Based on these fragments, we established a TaqMan MGB Real-time PCR method for detecting bacteria. We found that the method used in this study had the advantages of high sensitivity and good specificity.

Conclusions

The casx gene-based method of bacterial identification could be used as a supplement to the conventional 16 s rRNA-based detection method. This method has an advantage over the 16 s rRNA-based detection method in distinguishing the genetic relationship between closely-related bacteria, such as subgroup bacteria, and can be used as a supplement to the 16 s rRNA-based detection method.

The use of non-rodent model species in microbiota studies

In recent years, tremendous advances have been made in our ability to characterize complex microbial communities such as the gut microbiota, and numerous surveys of the human gut microbiota have identified countless associations between different compositional attributes of the gut microbiota and adverse health conditions. However, most of these findings in humans are purely correlative and animal models are required for prospective evaluation of such changes as causative factors in disease initiation or progression. As in most fields of biomedical research, microbiota-focused studies are predominantly performed in mouse or rat models. Depending on the field of research and experimental question or objective, non-rodent models may be preferable due to better translatability or an inability to use rodents for various reasons. The following review describes the utility and limitations of several non-rodent model species for research on the microbiota and its influence on host physiology and disease. In an effort to balance the breadth of potential model species with the amount of detail provided, four model species are discussed: zebrafish, dogs, pigs, and rabbits.

Potential relevance of pig gut content transplantation for production and research

It is becoming increasingly evident that the gastrointestinal microbiota has a significant impact on the overall health and production of the pig. This has led to intensified research on the composition of the gastrointestinal microbiota, factors affecting it, and the impact of the microbiota on health, growth performance, and more recently, behavior of the host. Swine production research has been heavily focused on assessing the effects of feed additives and dietary modifications to alter or take advantage of select characteristics of gastrointestinal microbes to improve health and feed conversion efficiency. Research on faecal microbiota transplantation (FMT) as a possible tool to improve outcomes in pigs through manipulation of the gastrointestinal microbiome is very recent and limited data is available. Results on FMT in humans demonstrating the transfer of phenotypic traits from donors to recipients and the high efficacy of FMT to treat Clostridium difficile infections in humans, together with data from pigs relating GI-tract microbiota composition with growth performance has likely played an important role in the interest towards this strategy in pig production. However, several factors can influence the impact of FMT on the recipient, and these need to be identified and optimized before this tool can be applied to pig production. There are obvious inherent biosecurity and regulatory issues in this strategy, since the donor's microbiome can never be completely screened for all possible non-desirable microorganisms. However, considering the success observed in humans, it seems worth investigating this strategy for certain applications in pig production. Further, FMT research may lead to the identification of specific bacterial group(s) essential for a particular outcome, resulting in the development of banks of clones which can be used as targeted therapeutics, rather than the broader approach applied in FMT. This review examines the factors associated with the use of FMT, and its potential application to swine production, and includes research on using the pig as model for human medical purposes.

Humanizing the gut microbiota of mice: Opportunities and challenges

Mouse colonized with human fecal microbiota is an interesting model concept with pros and cons like any other model system. The concept provides an ecologically relevant context to study food component and drug metabolism, and is an invaluable tool for phenotype transfer studies to prove the role of the gut microbiota in health and disease. The major drawbacks are the difficulties with transferring certain components of the human microbiota to the recipient mice, and immunological abnormalities observed in these mice. There seem to be unexplored opportunities for trying to reduce these limitations, but careful evaluation of pros, cons and possible alternatives is still necessary.

The Effects of Deoxynivalenol and Zearalenone on the Pig Large Intestine. A Light and Electron Microscopy Study

The contamination of feed with mycotoxins results in reduced growth, feed refusal, immunosuppression, and health problems. Deoxynivalenol (DON) and zearalenone (ZEN) are among the most important mycotoxins. The aim of the study was to examine the effects of low doses of these mycotoxins on the histological structure and ultrastructure of the large intestine in the pig. The study was performed on 36 immature gilts of mixed breed (White Polish Big &times; Polish White Earhanging), which were divided into four groups administrated per os with ZEN at 40 &micro;g/kg BW, DON at 12 &micro;g/kg BW, a mixture of ZEN (40 &micro;g/kg BW) and DON (12 &micro;g/kg BW) or a placebo. The pigs were killed by intravenous overdose of pentobarbital after one, three, and six weeks of treatment. The cecum, ascending and descending colon samples were prepared for light and electron microscopy. Administration of toxins did not influence the architecture of the mucosa and submucosa in the large intestine. ZEN and ZEN + DON significantly decreased the number of goblet cells in the cecum and descending colon. The mycotoxins changed the number of lymphocytes and plasma cells in the large intestine, which usually increased in number. However, this effect differed between the intestine segments and toxins. Mycotoxins induced some changes in the ultrastructure of the mucosal epithelium. They did not affect the expression of proliferative cell nuclear antigen and the intestinal barrier permeability. The obtained results indicate that mycotoxins especially ZEN may influence the defense mechanisms of the large intestine.

Interactions between human microbiome, diet, enteric viruses and immune system: Novel insights from gnotobiotic pig research

Studies over the past few decades demonstrated that gnotobiotic (Gn) pigs provide an unprecedented translational model to study human intestinal health and diseases. Due to the high degree of anatomical, physiological, metabolic, immunological, and developmental similarity, the domestic pig closely mimics the human intestinal microenvironment. Also, Gn piglets can be efficiently transplanted with human microbiota from infants, children and adults with resultant microbial profiles remarkably similar to the original human samples, a feat consistently not achievable in rodent models. Finally, Gn and human microbiota-associated (HMA) piglets are susceptible to human enteric viral pathogens (including human rotavirus, HRV) and can be fed authentic human diets, which further increases the translational potential of these models. In this review, we will focus on recent studies that evaluated the pathophysiology of protein malnutrition and the associated dysbiosis and immunological dysfunction in neonatal HMA piglets. Additionally, we will discuss studies of potential dietary interventions that moderate the effects of malnutrition and dysbiosis on antiviral immunity and HRV vaccines in HMA pigs. Such studies provide novel models and novel mechanistic insights critical for development of drug interventions.

Integrative Physiology: At the Crossroads of Nutrition, Microbiota, Animal Physiology, and Human Health

Nutrition is paramount in shaping all aspects of animal biology. In addition, the influence of the intestinal microbiota on physiology is now widely recognized. Given that diet also shapes the intestinal microbiota, this raises the question of how the nutritional environment and microbial assemblages together influence animal physiology. This research field constitutes a new frontier in the field of organismal biology that needs to be addressed. Here we review recent studies using animal models and humans and propose an integrative framework within which to define the study of the diet-physiology-microbiota systems and ultimately link it to human health. Nutritional Geometry sits centrally in the proposed framework and offers means to define diet compositions that are optimal for individuals and populations.

Prevotella and Klebsiella proportions in fecal microbial communities are potential characteristic parameters for patients with major depressive disorder

BACKGROUND

The diagnosis of major depression disorder (MDD) and other mental disorders were depended on some subjective survey scales. There are confirmed relationship between the gut flora and the mental states of MDD patients.

METHODS

The V3-V4 region of the 16S rRNA gene was extracted from the fecal microbial communities in MDD patients, PCR amplified and sequenced on the Illumina Miseq platform.

RESULTS

More phylum Firmicutes, less Bacteroidetes, and more genus Prevotella, Klebsiella, Streptococcus and Clostridium XI were found in MDD patients. The changes of the proportion of Prevotella and Klebsiella were consistent with Hamilton depression rating scale.

LIMITATIONS

The conclusion was limited by small sample sizes and potential uncontrollable influence factors on fecal microbiota.

DISCUSSION

Prevotella and Klebsiella proportion in fecal microbial communities should be concerned in the diagnosis and therapeutic monitoring of MDD in future.

Lactobacillus rhamnosus GG modulates innate signaling pathway and cytokine responses to rotavirus vaccine in intestinal mononuclear cells of gnotobiotic pigs transplanted with human gut microbiota

Background

A better understanding of mechanisms underlying dose-effects of probiotics in their applications as treatments of intestinal infectious or inflammatory diseases and as vaccine adjuvant is needed. In this study, we evaluated the modulatory effects of Lactobacillus rhamnosus GG (LGG) on transplanted human gut microbiota (HGM) and on small intestinal immune cell signaling pathways in gnotobiotic pigs vaccinated with an oral attenuated human rotavirus (AttHRV) vaccine.

Results

Neonatal HGM transplanted pigs were given two doses of AttHRV on 5 and 15 days of age and were divided into three groups: none-LGG (AttHRV), 9-doses LGG (AttHRV + LGG9X), and 14-doses LGG (AttHRV + LGG14X) (n = 3–4). At post-AttHRV-inoculation day 28, all pigs were euthanized and intestinal contents and ileal tissue and mononuclear cells (MNC) were collected. AttHRV + LGG14X pigs had significantly increased LGG titers in the large intestinal contents and shifted structure of the microbiota as indicated by the formation of a cluster that is separated from the cluster formed by the AttHRV and AttHRV + LGG9X pigs. The increase in LGG titers concurred with significantly increased ileal HRV-specific IFN-γ producing T cell responses to the AttHRV vaccine reported in our previous publication, suggesting pro-Th1 adjuvant effects of the LGG. Both 9- and 14-doses LGG fed pig groups had significantly higher IkBα level and p-p38/p38 ratio, while significantly lower p-ERK/ERK ratio than the AttHRV pigs, suggesting activation of regulatory signals during immune activation. However, 9-doses, but not 14-doses LGG fed pigs had enhanced IL-6, IL-10, TNF-α, TLR9 mRNA levels, and p38 MAPK and ERK expressions in ileal MNC. Increased TLR9 mRNA was in parallel with higher mRNA levels of cytokines, p-NF-kB and higher p-p38/p38 ratio in MNC of the AttHRV + LGG9X pigs.

Conclusions

The relationship between modulation of gut microbiota and regulation of host immunity by different doses of probiotics is complex. LGG exerted divergent dose-dependent effects on the intestinal immune cell signaling pathway responses, with 9-doses LGG being more effective in activating the innate immunostimulating TLR9 signaling pathway than 14-doses in the HGM pigs vaccinated with AttHRV.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0727-2) contains supplementary material, which is available to authorized users.

Critical review evaluating the pig as a model for human nutritional physiology

The present review examines the pig as a model for physiological studies in human subjects related to nutrient sensing, appetite regulation, gut barrier function, intestinal microbiota and nutritional neuroscience. The nutrient-sensing mechanisms regarding acids (sour), carbohydrates (sweet), glutamic acid (umami) and fatty acids are conserved between humans and pigs. In contrast, pigs show limited perception of high-intensity sweeteners and NaCl and sense a wider array of amino acids than humans. Differences on bitter taste may reflect the adaptation to ecosystems. In relation to appetite regulation, plasma concentrations of cholecystokinin and glucagon-like peptide-1 are similar in pigs and humans, while peptide YY in pigs is ten to twenty times higher and ghrelin two to five times lower than in humans. Pigs are an excellent model for human studies for vagal nerve function related to the hormonal regulation of food intake. Similarly, the study of gut barrier functions reveals conserved defence mechanisms between the two species particularly in functional permeability. However, human data are scant for some of the defence systems and nutritional programming. The pig model has been valuable for studying the changes in human microbiota following nutritional interventions. In particular, the use of human flora-associated pigs is a useful model for infants, but the long-term stability of the implanted human microbiota in pigs remains to be investigated. The similarity of the pig and human brain anatomy and development is paradigmatic. Brain explorations and therapies described in pig, when compared with available human data, highlight their value in nutritional neuroscience, particularly regarding functional neuroimaging techniques.

Human microbiota-associated swine: current progress and future opportunities

Gnotobiotic (GN) rodent models have provided insight into the contributions of the gut microbiota to host health and preventing disease. However, rodent models are limited by several important physiological and metabolic differences from humans, and many rodent models do not dependably replicate the clinical manifestations of human diseases. Due to the high degree of similarity in anatomy, physiology, immunology and brain growth, the domestic pig (Sus scrofa) is considered a clinically relevant model to study factors influencing human gastrointestinal, immune, and brain development. Gnotobiotic piglet models have been developed and shown to recapitulate key aspects of GN rodent models. Human microbiota-associated (HMA) piglets have been established using inocula from infants, children, and adults. The gut microbiota of recipient HMA piglets was more similar to that of the human donor than that of conventionally reared piglets harboring a pig microbiota. Moreover, Bifidobacterium and Bacteroides, two predominant bacterial groups of infant gut, were successfully established in the HMA piglets. Thus, the HMA pig model has the potential to be a valuable model for investigating how the gut microbiota composition changes in response to environmental factors, such as age, diet, vaccination, antibiotic use and infection. The HMA also represents a robust model for screening the efficacy of pre- and probiotic interventions. Lastly, HMA piglets can be an ideal model with which to elucidate microbe-host interactions in human health and disease due to the similarities to humans in anatomy, physiology, developmental maturity at birth, and the pathophysiology of many human diseases.

The porcine innate immune system: an update

Over the last few years, we have seen an increasing interest and demand for pigs in biomedical research. Domestic pigs (Sus scrofa domesticus) are closely related to humans in terms of their anatomy, genetics, and physiology, and often are the model of choice for the assessment of novel vaccines and therapeutics in a preclinical stage. However, the pig as a model has much more to offer, and can serve as a model for many biomedical applications including aging research, medical imaging, and pharmaceutical studies to name a few. In this review, we will provide an overview of the innate immune system in pigs, describe its anatomical and physiological key features, and discuss the key players involved. In particular, we compare the porcine innate immune system to that of humans, and emphasize on the importance of the pig as model for human disease.

Development of gut immunoglobulin A production in piglet in response to innate and environmental factors

The current review focuses on pre- and post-natal development of intestinal immunoglobulin A (IgA) production in pig. IgA production is influenced by intrinsic genetic factors in the foetus as well as extrinsic environmental factors during the post-natal period. At birth, piglets are exposed to new antigens through maternal colostrums/milk as well as exogenous microbiota. This exposure to new antigens is critical for the proper development of the gut mucosal immune system and is characterized mainly by the establishment of IgA response. A second critical period for neonatal intestinal immune system development occurs at weaning time when the gut environment is exposed to new dietary antigens. Neonate needs to establish oral tolerance and in the absence of protective milk need to fight potential new pathogens. To improve knowledge about the immune response in the neonates, it is important to identify intrinsic and extrinsic factors which influence the intestinal immune system development and to elucidate their mechanism of action.

Probiotic Lactobacillus rhamnosus GG enhanced Th1 cellular immunity but did not affect antibody responses in a human gut microbiota transplanted neonatal gnotobiotic pig model

This study aims to establish a human gut microbiota (HGM) transplanted gnotobiotic (Gn) pig model of human rotavirus (HRV) infection and diarrhea, and to verify the dose-effects of probiotics on HRV vaccine-induced immune responses. Our previous studies using the Gn pig model found that probiotics dose-dependently regulated both T cell and B cell immune responses induced by rotavirus vaccines. We generated the HGM transplanted neonatal Gn pigs through daily feeding of neonatal human fecal suspension to germ-free pigs for 3 days starting at 12 hours after birth. We found that attenuated HRV (AttHRV) vaccination conferred similar overall protection against rotavirus diarrhea and virus shedding in Gn pigs and HGM transplanted Gn pigs. HGM promoted the development of the neonatal immune system, as evidenced by the significantly enhanced IFN-γ producing T cell responses and reduction of regulatory T cells and their cytokine production in the AttHRV-vaccinated pigs. The higher dose Lactobacillus rhamnosus GG (LGG) feeding (14 doses, up to 109 colony-forming-unit [CFU]/dose) effectively increased the LGG counts in the HGM Gn pig intestinal contents and significantly enhanced HRV-specific IFN-γ producing T cell responses to the AttHRV vaccine. Lower dose LGG (9 doses, up to 106 CFU/dose) was ineffective. Neither doses of LGG significantly improved the protection rate, HRV-specific IgA and IgG antibody titers in serum, or IgA antibody titers in intestinal contents compared to the AttHRV vaccine alone, suggesting that an even higher dose of LGG is needed to overcome the influence of the microbiota to achieve the immunostimulatory effect in the HGM pigs. This study demonstrated that HGM Gn pig is an applicable animal model for studying immune responses to rotavirus vaccines and can be used for studying interventions (i.e., probiotics and prebiotics) that may enhance the immunogenicity and protective efficacy of vaccines through improving the gut microbiota.

Use of pigs as a potential model for research into dietary modulation of the human gut microbiota

The human intestinal microbial ecosystem plays an important role in maintaining health. A multitude of diseases including diarrhoea, gastrointestinal inflammatory disorders, such as necrotising enterocolitis (NEC) of neonates, and obesity are linked to microbial composition and metabolic activity. Therefore, research on possible dietary strategies influencing microbial composition and activity, both preventive and curative, is being accomplished. Interest has focused on pre- and probiotics that stimulate the intestinal production of beneficial bacterial metabolites such as butyrate, and beneficially affect microbial composition. The suitability of an animal model to study dietary linked diseases is of much concern. The physiological similarity between humans and pigs in terms of digestive and associated metabolic processes places the pig in a superior position over other non-primate models. Furthermore, the pig is a human-sized omnivorous animal with comparable nutritional requirements, and shows similarities to the human intestinal microbial ecosystem. Also, the pig has been used as a model to assess microbiota–health interactions, since pigs exhibit similar syndromes to humans, such as NEC and partly weanling diarrhoea. In contrast, when using rodent models to study diet–microbiota–health interactions, differences between rodents and humans have to be considered. For example, studies with mice and human subjects assessing possible relationships between the composition and metabolic activity of the gut microbiota and the development of obesity have shown inconsistencies in results between studies. The present review displays the similarities and differences in intestinal microbial ecology between humans and pigs, scrutinising the pig as a potential animal model, with regard to possible health effects.

Porcine intestinal mast cells. Evaluation of different fixatives for histochemical staining techniques considering tissue shrinkage

Staining of mast cells (MCs), including porcine ones, is critically dependent upon the fixation and staining technique. In the pig, mucosal and submucosal MCs do not stain or stain only faintly after formalin fixation. Some fixation methods are particularly recommended for MC staining, for example the fixation with Carnoy or lead salts. Zinc salt fixation (ZSF) has been reported to work excellently for the preservation of fixation-sensitive antigens. The aim of this study was to establish a reliable histological method for counting of MCs in the porcine intestinum. For this purpose, different tissue fixation and staining methods that also allow potential subsequent immunohistochemical investigations were evaluated in the porcine mucosa, as well as submucosa of small and large intestine. Tissues were fixed in Carnoy, lead acetate, lead nitrate, Zamboni and ZSF and stained subsequently with either polychromatic methylene blue, alcian blue or toluidine blue. For the first time our study reveals that ZSF, a heavy metal fixative, preserves metachromatic staining of porcine MCs. Zamboni fixation was not suitable for histochemical visualization of MCs in the pig intestine. All other tested fixatives were suitable. Alcian blue and toluidine blue co-stained intestinal goblet cells which made a prima facie identification of MCs difficult. The polychromatic methylene blue proved to be the optimal staining. In order to compare MC counting results of the different fixation methods, tissue shrinkage was taken into account. As even the same fixation caused shrinkagedifferences between tissue from small and large intestine, different factors for each single fixation and intestinal localization had to be calculated. Tissue shrinkage varied between 19% and 57%, the highest tissue shrinkage was found after fixation with ZSF in the large intestine, the lowest one in the small intestine after lead acetate fixation. Our study emphasizes that MC counting results from data using different fixation techniques can only be compared if the respective studyimmanent shrinkage factor has been determined and quantification results are adjusted accordingly.

Dietary supplementation with Bifidobacterium lactis NCC2818 from weaning reduces local immunoglobulin production in lymphoid-associated tissues but increases systemic antibodies in healthy neonates

Weaning is associated with a major shift in the microbial community of the intestine, and this instability may make it more acquiescent than the adult microbiota to long-term changes. Modulation achieved through dietary interventions may have potentially beneficial effects on the developing immune system, which is driven primarily by the microbiota. The specific aim of the present study was to determine whether immune development could be modified by dietary supplementation with the human probiotic Bifidobacterium lactis NCC2818 in a tractable model of weaning in infants. Piglets were reared by their mothers before being weaned onto a solid diet supplemented with B. lactis NCC2818, while sibling controls did not receive supplementation. Probiotic supplementation resulted in a reduction in IgA (P<0·0005) and IgM (P<0·009) production by mucosal tissues but had no effect on IgG production (P>0·05). Probiotic-supplemented pigs had more mast cells than unsupplemented littermates (P<0·0001), although numbers in both groups were low. In addition, the supplemented piglets made stronger serum IgG responses to fed and injected antigens (P<0·05). The present findings are consistent with B. lactis NCC2818 reducing intestinal permeability induced by weaning, and suggest that the piglet is a valuable intermediate between rodent models and human infants. The results also strongly suggest that measures of the effect of probiotic supplementation on the immune system need to be interpreted carefully as proxy measures of health benefit. However, they are useful in developing an understanding of the mechanism of action of probiotic strains, an important factor in predicting favourable health outcomes of nutritional intervention.

A defined intestinal colonization microbiota for gnotobiotic pigs

Maximising the ability of piglets to survive exposure to pathogens is essential to reduce early piglet mortality, an important factor in efficient commercial pig production. Mortality rates can be influenced by many factors, including early colonization by microbial commensals. Here we describe the development of an intestinal microbiota, the Bristol microbiota, for use in gnotobiotic pigs and its influence on synthesis of systemic immunoglobulins. Such a microbiota will be of value in studies of the consequences of early microbial colonization on development of the intestinal immune system and subsequent susceptibility to disease. Gnotobiotic pig studies lack a well-established intestinal microbiota. The use of the Altered Schaedler Flora (ASF), a murine intestinal microbiota, to colonize the intestines of Caesarean-derived, gnotobiotic pigs prior to gut closure, resulted in unreliable colonization with most (but not all) strains of the ASF. Subsequently, a novel, simpler porcine microbiota was developed. The novel microbiota reliably colonized the length of the intestinal tract when administered to gnotobiotic piglets. No health problems were observed, and the novel microbiota induced a systemic increase in serum immunoglobulins, in particular IgA and IgM. The Bristol microbiota will be of value for highly controlled, reproducible experiments of the consequences of early microbial colonization on susceptibility to disease in neonatal piglets, and as a biomedical model for the impact of microbial colonization on development of the intestinal mucosa and immune system in neonates.

Assessment of the modulating effects of fructo-oligosaccharides on fecal microbiota using human flora-associated piglets

We first used human flora-associated (HFA) piglets, a significantly improved model for research on human gut microbiota, to study the effects of short-chain fructo-oligosaccharides (scFOS) on the gut bacterial populations. Ten neonatal HFA piglets were assigned to receive basal diets alone or supplemented with scFOS (0.5 g/kg body weight/day) from 1 to 37 days after birth (DAB). The impact of scFOS on the fecal bacterial populations of the piglets before (12 DAB), during (17 DAB), and after (25 and 37 DAB) weaning were monitored by PCR-denaturing gradient gel electrophoresis and real-time quantitative PCR. The Bifidobacterium genus was stimulated consistently, except during weaning, confirming the bifidogenic property of scFOS. At 12 DAB, the Clostridium leptum subgroup was decreased and two unknown Bacteroides-related species were increased; at 25 DAB, the C. leptum subgroup and Subdoligranulum variabile-like species were elevated, whereas one unknown Faecalibacterium-related species was suppressed; and at 37 DAB, the Bacteroides genus was decreased. The results showed that effects of scFOS on non-bifidobacteria varied at different developmental stages of the animals, warranting further investigation into the host-development-related effects of prebiotics on the gut microbiota and the host physiology using the HFA piglets as a model for humans.

Role of postnatal acquisition of the intestinal microbiome in the early development of immune function

OBJECTIVES

Therapy with broad-spectrum antibiotics is a common practice for premature infants. This treatment can reduce the biodiversity of the fecal microbiota and may be a factor in the cause of necrotizing enterocolitis. In contrast, probiotic treatment of premature infants reduces the incidence of necrotizing enterocolitis. We hypothesized that 1 mechanism for these observations is the influence of bacteria on postnatal development of the mucosal immune system.

MATERIALS AND METHODS

Expression of immune molecules and microbial sensors was investigated in the postnatal mouse gastrointestinal tract by real-time polymerase chain reaction. Subsequently, 2-week-old specific pathogen-free and microbial-reduced (MR; antibiotic treated) mice were compared for immune molecule and microbial sensor expression, mesenteric lymph node T-cell numbers and activation, intestinal barrier function/permeability, systemic lymphocyte numbers, and T-cell phenotype commitment.

RESULTS

Toll-like receptor 2, 4, and 5 expression was highest in 2-week-old specific pathogen-free mice, and this expression was decreased in MR mice. There was no difference in intestinal tight-junctional function, as evaluated by fluorescein isothiocyanate-dextran uptake, but MR mice had increased bacterial translocation across the intestinal epithelial barrier. MR mice had significantly fewer splenic B cells and mesenteric lymph node CD4+ T cells, but there were normal numbers of splenic T cells. These systemic T cells from MR mice produced more interleukin-4 and less interferon-gamma and IL-17, indicative of maintenance of the fetal, T-helper cell type 2 phenotype.

CONCLUSIONS

The present study shows that intestinal commensal microbiota have an influence on early postnatal immune development. Determining specific bacteria and/or bacterial ligands critical for this development could provide insight into the mechanisms by which broad-spectrum antibiotics and/or probiotic therapy influence the development of the mucosal immune system and mucosal-related diseases.

Ageing and its possible impact on mucosal immune responses

The development, structural diversification, and functional maturation of mammalian immunologic repertoire at mucosal surfaces and the systemic lymphoid tissue is a remarkably dynamic and continuous process, which begins in early fetal life and eventually culminates in variable degree of senescence or cellular death with advancing age. This brief overview will highlight the status of our current understanding of the ontogeny of mucosal immunologic response. The role of mucosal microflora and other environmental macromolecules in the regulation of mucosal immunity relative to the process of ageing will also be reviewed.